The Crown Graphic is a good option. On the plus side, it is light and very durable. I don't think anyone has mentioned this so far, but you can use it hand-held (although, like any other large camera, anything under 1/125 and you are taking your chances). You can use a pair of Grafmatic holders and have more than enough sheets for one outing. On the minus side, it has very few movements. You say you like landscapes, in which case, front tilt is often very useful. There is a simple mod you can do to a Crown to get front tilt.

If you want more movements, the Super Graphic is a good option. It is slightly heavier than the Crown but has a metal body which is almost indestructible. It has as much front movement as just about any field camera. It has no back movements but the back does rotate 360. It is a great camera. Although I now use a full field camera, I have used both the Crown and the Super in the field quite a bit and, except for the limits I mentioned, they really do the job.

The main advantages of LF over MF are: 1) you can develop each negative individually, and 2) movements. If neither of these is important to you, then stick then stick with medium format. MF is a huge step over 35mm and unless you are doing very large prints, you won't be able to tell the difference between 120 and 4x5. The perfect MF camera for you, in my opinion, is the Mamiya 7 (there are a few variations). It is not cheap but it is one helluva camera. If that is not in the budget, then go with a vintage folder with a good lens. Honestly, LF has its distinct advantages but the context (mountain biking) is not going to allow you to explore them easily, Keep in mind that with 4x5, you have to setup and takedown every time you stop for a different shot.